This invention relates to an apparatus for the pulping of wood and other ligno-cellulosic materials and more particularly to screw feeders for conveying such materials, as for example, wood chips, sawdust and the like.
Since the invention of the thermo-mechanical pulping process in the 1930's, see, for example, U.S. Pat. No. 2,145,851 to Asplund, defibrating processes and apparatus for the production of pulp have found increasingly wide spread commercial use. In such processes and apparatus, ligno-cellulosic materials, such as wood chips, shavings and sawdust or nonwood fibers such as sugar cane bagasse, are fed from a hopper or storage bin to screw feeder means to further processing equipment which may include mechanical defibrators or other disc refiners, digesters and other known pulping devices. Trouble-free operation of the screw feeder is desirable in order to maintain throughput of material and continuity of the process to obtain acceptable yields.
Nevertheless, it has been found that spiral screw feed conveyors experience plugging which interupts the uniform flow of material through the apparatus and results in costly machinery down time. Such clogging of the screw feeder may especially occur when the pulping apparatus is employed for the processing of finer materials such as wood chips, bark, shavings, sawdust, sugar cane bagasse and other wet, pitchy and gummy materials. While the use of grooved barrels in screw feeder throats has helped to reduce aspects of this problem, the inlet end of the throat still experiences plugging and results in overloading conditions.